Question 1

Which of the following best describes the difference between homolytic and heterolytic bond cleavage?

Accepted Answer

Homolytic cleavage results in the formation of free radicals, while heterolytic cleavage results in the formation of ions.

Question 2

Consider the following reaction: $$\mathrm{CH_4$ + Cl_2$ \xrightarrow{hv} CH_3Cl + HCl}. $$Which step in the free radical chain mechanism is responsible for generating the first chlorine radical?

Accepted Answer

Initiation step

Question 3

Which of the following statements about the rate-limiting step in a multistep reaction is correct?

Accepted Answer

It determines the overall rate of the reaction.

Question 4

According to the Hammond Postulate, the transition state of an exothermic reaction most closely resembles:

Accepted Answer

The reactants in both energy and structure.

Question 5

Which of the following best explains why bromination of propane is more selective than chlorination?

Accepted Answer

Bromination is endothermic, so the transition state is product-like and more sensitive to product stability.

Question 6

Which of the following is the correct order of stability for free radicals?

Accepted Answer

$$\mathrm{3^\circ \u003e 2^\circ \u003e 1^\circ \u003e methyl}$$

Question 7

In the chlorination of methane, which of the following is a termination step?

Accepted Answer

Two chlorine radicals combine to form $$\mathrm{Cl_2$}.$$

Question 8

Which of the following statements about reaction-energy diagrams is correct?

Accepted Answer

The activation energy ($$E_a) is $$the energy difference between the reactants and the transition state.

Question 9

A reaction has $$E_a = +17\ \mathrm{kJ/mol}$$ and $$\Delta H^\circ = +4\ \mathrm{kJ/mol}. $$Which of the following best describes this reaction?

Accepted Answer

It is endothermic and has a product-like transition state.

Question 10

Which of the following is NOT a reactive intermediate discussed in the study materials?

Accepted Answer

Alkene

Question 11

Which of the following best describes the role of thermodynamics in chemical reactions?

Accepted Answer

It allows us to compare the stability of reactants and products and predict equilibrium favorability.

Question 12

Which of the following is a correct statement about the propagation steps in the free radical chlorination of methane?

Accepted Answer

The second propagation step regenerates a chlorine radical.

Question 13

Which of the following best explains why reactive intermediates are never present in high concentrations?

Accepted Answer

They react as quickly as they are formed.

Question 14

Which of the following is true regarding the selectivity of halogenation reactions?

Accepted Answer

Bromination is more selective than chlorination because its transition state is more product-like.

Question 15

Which of the following is the correct equation for the homolytic cleavage of a chlorine molecule?

Accepted Answer

$$\mathrm{Cl_2$ \rightarrow 2\ Cl\cdot}$$

Question 16

Which of the following best describes the effect of a termination step in a free radical chain reaction?

Accepted Answer

It slows or stops the chain reaction by consuming free radicals.

Study Guide: The Study of Chemical Reactions (Organic Chemistry)

Study Guide - Practice Questions

Study Guide - Flashcards